Ventilator

ABSTRACT

A ventilator capable of both pressure-cycled and volume-cycled operation. A main valve connects a gas supply conduit to a downstream conduit when the pressure in a command signal conduit reaches a first predetermined pressure level and closes off the downstream conduit from the gas supply conduit when the pressure in the command signal conduit drops below a second predetermined pressure level. In the expiratory cycle, the command signal conduit and the downstream conduit are bled to atmospheric. The inspiratory cycle may be initiated (1) by the patient breathing in and thereby lowering airway pressure, or (2) after a time lapse following the commencement of said expiratory phase, the duration of said time lapse being determined as a set multiple of the time of the preceding inspiratory phase. The expiratory phase may be initiated (1) by the achievement of a predetermined airway pressure or (2) upon the delivery of a predetermined volume of gas.

I United States Patent 1151 3,669,108 Sundblom et al. 1 1 June 13, 1972[54] VENTILATOR Primary Examiner-Charles F. Rosenbaum AssistantExaminerJ. B. Mitchell [72] Inventors: Leif J. Sundblom, Castro Valley;Louis A.

OHM", Menlo Park both of Calif. Attorney-Owen, W1ckersham & Erlckson[73] Assignee: Veriflo Corporation, Richmond, Calif. ABSTRACT [22]Filed; O t, 20, 1969 A ventilator capable of both pressure-cycled andvolume-cyled ti A al 1 1 PP 861,804Zd053552afi'conifiiihelifiil'liiiiiii ififiiinii'i sigifii conduitreaches a first predetermined pressure level and 52 us. 01. ..l28/l45.8128/1422 Closes Off the downstream nduit from the gas supply conduit is1 1 1m. c1. .A62b 7/02 when Press"re the comma signal conduit drops belw[58] Field of Search ..12s/145.s, 1455-1451, sewnd predeterminedPressure "Piramry 128/! 4 145 cle, the command signal conduit and thedownstream conduit are bled to atmospheric. The inspiratory cycle may bein- [56] References Cited itiated (l) by the patient breathing in andthereby lowering airway pressure, or (2) after a time lapse followingthe com- UNITED STATES TENTS mencement of said expiratory phase, theduration of said time lapse being determined as a set multiple of thetime of the 3,265,061 8/1966 Gage ..l28/ 145.8 preceding inspiratoryphase. The expiratory phase may be 3,114,365 12/1963 Franz itiated (l)by the achievement of a redetermined airwa 1 s 145 s p y 3 3 7/ 1967Bird at 2 pressure or (2) upon the delivery of a predetermined volume3,504,670 4/1970 l-loel ...l28/l45.8 ofgas 3,434,471 3/1969 Liston..l28/l45.8

45 Claims, 18 Drawing Figures PRESSURE 0 1 VOLUME CYCLE o INIT- 62oRAT'O INSPIRATORY PRES-S SGHS TIME 285 VOLUME 1760' SmH MAN AL 3010 AilT 328% 113 k 'PATE'NTEDJun13I912 I 1 3.669108 sum o1nF12 LV-I FIG'ICINVENTORS LEIF J. SUNDBLOM LOUIS A. OLLIVIER a/Mbzw ATTORNFYSPAIENTEDJuu 13 m2 sum 02 or 12 GAS FIG/I8 FIGJC INVENTORS SUNDBLOMATTORNEYS PATENTEDJuu 13 I972 sum on or 12 @IRMY PRESSURE 62a NEGRATlOTIME VOLUME PRES'S. SIGHS )4 176d"@ 285 237a I INIT MH 328 1 I Fl 6. 3

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PATENTEDJuu 1 3 m2 3. 869. 1 O8 sum 05 [1F 12 INVENTORS LEIF J. SUNDBLOMBY LOUIS A. OLLIVIER 00M, 38 .44.

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INVENTORfi' LEIF J. SUNDBLOM BY LOUIS A. OLLIVIER ATTORNEYS PATENTEDwmmz8.669.108

sum uaor12 INVENTOR5 LEIF J. SUNDBLON BY LOUIS A. OLLIVIER 0am, MM 8ATTORNEYS PATENTEnJun 13 m2 3. 669. 1 08 SHEET 09UF12 237 FIG. 9 275ATTORNEYS INVENTGRS LEIF J. SUNDBLOM PATENTEDJummn I 3.669.108

sum 12UF12 INVENTORS LEIF J. SUNDBLOM BY LOUIS A. OLLIVIER 00m, ll/ulmlhi ATTORNEYS VENTILATOR This invention relates to an improved ventilatorcapable of both pressure-cycled and volume-cycled operation. Can beeither Pressure-cycled or Volume-cycled Ventilators heretofore on themarket have either been pressure-cycled or volume-cycled and have notbeen capable of shifting from one form of operation to the other, as isthe device of the present invention, where simple movement of a selectorhandle accomplishes the shift. Hence, prior-art ventilators werestrictly limited to one of these two types of operation and extramachines were required. The present invention enables a single machineto become very versatile and to be adapted to the needs of the patientand to the desires of the doctor. Moreover, as will be seen, theventilator of this invention also gives greater versatility within eachtype of operation than has been available from prior-art machines.

F low Pattern Adjustable Another difficulty with the ventilatorsheretofore on the market has been that their flow pattern of deliveryhas been capable of little, if any, adjustment; each has had a basicallyfixed flow pattern. It is desirable to have a large initial flow at thebeginning of the inspiratory phase and to have the flow graduallydiminish toward a predetermined minimum flow at the end of theinspiratory phase.

The ventilator of the present invention enables a wide range ofadjustment of the flow pattern, and any such flow pattern isreproducible independently of the time setting of the cycle. The maximuminitial flow can be adjusted to a desired amount, the smaller terminalflow at the end can be adjusted to what is desired, and the change fromone to the other adjusted too.

Automatic Ratio of Inspiratory Time to Expiratory Time The ventilator ofthis invention also provides for setting a ratio between the inspiratorytime and either the maximum or the actual expiratory time in thebreathing cycle. This adjustment, once set, is maintained untilpurposely reset, but a wide range of such ratios is readily obtainable.Thus, this ratio setting enables full control of the patients breathingcycle on the basis that the longer it takes to inhale, the longer ittakes to exhale, and each inspiration controls the succeedingexpiration, and a new inspiratory phase is initiated at the right time.This same ratio setting can be used as a backup expedient when a patientnormally initiates each inspiratory phase himself but if he fails to doso within a time bearing the set ratio to his previous inspiration, themachine will itself begin the new inspiratory phase.

Independent Setting of inspiratory Time and Tidal Volume In itsvolume-cycled mode the ventilator of this invention is also capable of aseparate noninteracting adjustment of the total volume and theinspiratory time, so that either the time or the volume can be changedwithout changing the other, whereas heretofore adjustment of one wouldrequire adjustment of the other, each time a change is made. In thisinvention there is a novel interaction of parts that automatically caresfor these adjustments.

Pressure Sensitivity and Safety When the device is used in itspressure-cycled mode, the airway pressure is employed to sense apatients initiation of a new inspiratory phase and then to feed thebreathing gas to him at a doctor-set rate and manner. In addition, theairway pressure is used to terminate the inspiratory phase and commencean expiratory phase. Furthermore, in both the pressure-cycled andvolume-cycled modes of operation, patient safety is assured by apressure-activated safety release that terminates the inspiratory phasebefore a dangerous airway pressure is reached. Manual Override In bothvolume-cycled and pressure-cycled operation the doctor can readilyoverride and initiate a new inspiratory phase manually simply bypressing a button provided for that purpose.

Supply Pressure and Gas Mixture Versatility A significant object of theinvention is to provide a ventilator that can be used with relativelylow pressures, such as 25 psig supply pressure, instead of requiring asupply at 50 psig, or higher.

Many optional features are also available in this ventilator, such as achange from pure oxygen to air-diluted oxygen, the use of so-callednegative pressure" where that is desirable and the elimination of itwhere it is not, and the adjustment of many other factors.

The ventilator of this invention is supplied with a compressed gas suchas oxygen, air or a premix of air and oxygen at a regulated pressure,typically of approximately 50 psi, though that may be varied. When usingoxygen as the supply gas the ventilator of this invention will deliverpure oxygen or an oxygen-air mixture in the pressure-cycled" mode. Inthe volume-cycled mode, the ventilator will deliver pure oxygen only.When using air as the supply gas, the ventilator will deliver air inboth the pressure-cycled and volume-cycled modes. When using mixtureobtainable from an oxygen ratio controller, the ventilator will deliverthe same oxygen-air mixture as that supplied in either pressure-cycledor volume-cycled modes.

Sigh

In normal breathing, from time to time a person will take anexceptionally deep breath and then exhale that deep breath. This sigh isquite useful in maintaining healthy conditions. Most breathing machinesmake no provision for other than consistent uniformity. The device ofthe present invention makes it possible for the doctor to cause a sighat suitable intervals, super-imposing the sigh on the regular cyclewithout upsetting subsequent regular cycling until the next sigh.

Other objects and advantages of the invention will appear from thefollowing description of a preferred form of the invention.

In the drawings:

FIGS. 1A, 1B, and 1C comprise a pneumatic circuit diagram of aventilator embodying the principles of the present invention. The threeviews fit together and comprise a single diagram.

FIG. 2 is a view in perspective of the exterior of a ventilator unitembodying the principles of the invention.

FIG. 3 is a view on an enlarged scale and in front elevation of apreferred embodiment of the main control valve from the circuit of FIG.18, being a component of the unit of FIG. 2.

FIG. 4 is a view in rear elevation of the valve of FIG. 3.

FIG. 5 is a view section taken along the line 5-5 in FIGS. 3 and 4.

FIG. 6 is a view in elevation and in section, on an enlarged scale, of apreferred embodiment of the initiator or sensitivity control valve usedin the circuit of FIG. 18.

FIG. 7 is a view in elevation and in section, on an enlarged scale, of apreferred embodiment of the pressure controller of the circuit of FIG.1B.

FIG. 8 is a view in elevation and in section, on an enlarged scale, of apreferred embodiment of the volume profile regulator of FIG. 1A.

FIG. 9 is a top view, partly broken away and shown in section, on anenlarged scale, of a preferred embodiment of the volume control unit ofFIG. 1A.

FIG. 10 is a view in section taken along the line 10-10 in FIG. 9.

FIG. 11 is a view in section taken along the line 11-11 in FIG. 10.

FIGS. 12A, 12B, 12C, and 12D are diagrammatic views showing theoperation of the compensator port with respect to the volume port atextreme settings of the volume and inspiratory time control shafts, allfor the unit of FIGS. 9 to 11.

FIG. 13 is a view in section taken along the line 13-13 in FIGS. 9 and10.

THE SELECTOR VALVE ASSEMBLY 12 (FIG. 1B)

In FIG. 1B a supply 10 of oxygen at some desired pressure is provided.The supply 10 may include a regulator or other device to provide thedesired pressure, and the oxygen supplied may be pure oxygen or air or amixture of oxygen and air. For that matter, other gases may be used ifdesired. The supply 10 is connected by a conduit 11 to a manuallyoperated valve assembly 12 at an inlet 13. The valve assembly isoperated by a valve control lever or selector 12a shown in FIG. 2.

The valve assembly 12 is preferably provided with five valves, each ofwhich has three positions, an 011" position, a pressure-cycled"position, and a volume-cycled" position. Thus, the assembly 12 includesa valve 14 connected to the inlet 13, which either shuts off the supplyof oxygen from the conduit 11 or, in the volume-cycled mode, sends it toa volume-cycled outlet 15 or, in a pressure-cycled mode, sends it to apressure-cycled" outlet 16. The outlets l and 16 are connected to a maininternal supply conduit 20. Since the outlets 15 and 16 are connectedtogether, the valve 14 acts substantially as an off-on" valve, eitherpassing the full supply of oxygen or cutting it off completely, but thestructure shown is preferred in order to provide a simple gangedassembly 12, that is, the valve 14 is ganged with valves 17, 18, 19, and29 for movement of all of them together between these three positions;either all of valves 14, 17, 18, 19, and 29 are in off position, or allof them are in the pressure-cycled" position, or all of them are in thevolume-cycled" position.

The second valve 17 of the valve assembly 12 has an inlet 21 which isalways connected to the main conduit 20 and which is connectedalternately to a volume-cycled outlet 22 or a pressure-cycled outlet 23or is blocked in an off position. Like the first valve 14, the secondvalve 17 is operative in both the pressure-cycled and volume-cycledmodes.

The third valve 18 of the valve assembly 12 has an inlet 24 which iseither connected to a pressure-cycled" outlet 25 or is blocked off inboth its off position and its volumecycled position. In other words, thevalve 18 is operative only in the pressure-cycled mode.

The fourth valve 19 of the valve assembly 12 has an inlet 26, avolume-cycled" outlet 27 and a "pressure-cycled outlet 28, and thefourth valve is operative in both the pressure-cycled and volume-cycledmodes.

The fifth valve 29 of the valve assembly 12 has an inlet 85 connected inthe volume-cycled mode alone to an outlet 86 that leads directly to theatmosphere. There are no inlets in the of position or thepressure-cycled mode; so the fifth valve 29 is operative only in thevolume-cycled mode.

It is stressed that all of the valves in the assembly 12 are linkedtogether for simultaneous operation, so that all of them are either off,are in the volume-cycled" position, or in the pressure-cycled position.It has been noted that the valves 14, 17, and 19 are operative in bothmodes, the valve 19 operative only in the pressure-cycled mode and thevalve 29 operative only in the volume-cycled.

THE MAIN VALVE 30 (FIGS. 1B and 3-5) The internal supply conduit 20leads to a main valve 30 at a normally closed inlet 31; when a closuremember 32 is retracted from an opening 33, oxygen from the conduit 20can pass via an outlet 34 to a downstream conduit 35.

The closure member 32 is secured to two diaphragms 36 and 37, whichcooperate with the housing assembly 38 to divide the interior of themain valve 30 into three chambers 39, 40, and 41. The housing 38 (FIG.5) is so constructed that the diaphragm 36 has a significantly smallerarea exposed to the gas than does the diaphragm 37. The chamber 39 liesbetween the smaller area diaphragm 36 and the inlet 31 and outlet 34;this chamber 39 is used for the passage of the supply gas. In betweenthe two diaphragms 36 and 37, the chamber 40 is provided with a port 42that communicates with a command signal conduit 43. The third chamber 41is kept at atmospheric pressure by an atmospheric bleed port 44 andcontains a spring 45 which urges the diaphragms 36 and 37 and the clo'sure member 32 toward the closed position. As shown in FIGS. 3 to 5,bolts 46 may be used both to hold the housing assembly 38 together andto mount the valve 30 to a support member 47, shown in phantom lines.

The spring 45 acts to keep the closure member 32 against the inlet port31 until the pressure in the chamber 40 and the command signal conduit43 rises above a predetermined value (e.g., 18 psig), well aboveatmospheric pressure. Then, the fact that the pressure in the chamber 40acts on a larger area on the diaphragm 37 than on the diaphragm 36,causes the diaphragm 37 to move toward the chamber 41 and thereby movethe closure member 32 away from the inlet 31. As soon as thehigh-pressure gas from the conduit 20 begins entering the inlet 31 andflowing into the chamber 39, it acts on the diaphragm 36, and thus boththe diaphragm 36 and 37 are then causing the closure member 32 to open.The result is that once the critical pressure in the chamber 40 andcommand signal conduit 43 is reached, the main valve 30 opens the inletvery quickly in what is, in effect, a snap action. The inlet 3] thensends gas from the main conduit 20 into the downstream conduit 35.

In order for the closure member 32 to close off the inlet 31, thepressure in the chamber 40 and in the command signal conduit 43 mustdrop to a predetermined level well below the pressure that opens theinlet 31, e.g., 9 psig. As will be seen the conduit 43 is bled toatmosphere, and when the pressure level does fall below this second,lower, critical level, the closure member 32 does close the inlet 31.Subsequently, as will be seen, the pressure in the downstream conduit isbled toward atmospheric.

THE DOWNSTREAM CONDUIT 35 (FIGS. 1A and 1B) The downstream conduit 35communicates directly with the valve 19 at its inlet 26. The effects ofthis connection, which accomplish one of the main functions of thedownstream conduit 35, are explained later. The downstream conduit 35also communicates directly, as by branch conduits, with a check valve 48and a first pressure relief valve 50, both to be described later.Further, as shown in FIG. 1A, the conduit 35 communicates with a secondpressure relief valve 51, the function of which is also explained later.Still further, the conduit 35 communicates by an inlet 53 with a chamber54in a negative-pressure" control valve 55; the internal supply conduit20 also communicates with the negative pressure control valve 55 throughan inlet port 56 leading into a chamber 57 on the opposite side of adiaphragm 58 from the chamber 54. This valve, too, is dealt with furtherbelow. Finally, the downstream conduit 35 also communicates with a sighdevice 300 (FIG. 1C).

THE AUTOMATIC RATIO EXPIRATORY TIMER (FIG. 1B)

The command signal conduit 43 and the internal supply conduit 20 areconnected to an automatic ratio expiratory timer 60. The purpose of thisdevice is to conclude the expiratory phase of operation quite positivelyand to initiate a new inspiratory phase, in the event the patient doesnot do so himself by actuating the initiator discussed in the nextsection. In other words, the expiratory phase is either terminated inevery cycle by this timer 60 or at least it is always there to set amaximum time limit for the expiratory phase. This time, moreover, is nota time constant, since it takes longer to exhale after a long-drawnbreath than to exhale a shorter-drawn breath. Hence, the timerdetermines the maximum length of each expiratory phase as a set ratio tothe length of the immediately preceding inspiratory phase. The set ratiois, itself, set by the physician and can be changed at his order.

The automatic ratio expiratory timer 60 (FIG. 18) comprises a principalvalve 61, the check valve 48, the relief valve 50 and a needle valve 62,regulated by the control 62a in FIG. 2.

The valve 61 has three chambers 63, 64, and 65 provided by twodiaphragms 66 and 67, the diaphragm 67 having a much larger exposed areathan the diaphragm 66 (compare the valve 30). The first chamber 63 isconnected by an inlet 68 to the main inlet conduit 20. The twodiaphragms 66 and 67 are both rigidly connected to a closure member 70,which a spring 69 normally urges to close a port 71. When the port 71 isopened, it connects the chamber 63 to the command signal conduit 43. Thesmaller area diaphragm 66 which closes the chamber 63 cooperates withthe larger area diaphragm 67 to provide the central chamber 64, which isbled to atmosphere at all times through a port 72. On the opposite sideof the large diaphragm 67, is the chamber 65 which has two ports 73 and74. The port 73 is connected to the check valve 48 through a restrictedorifice 75.

The port 74 is connected to an inlet 76 of the pressure relief valve 50,on the opposite side of a diaphragm 77 from a port 78 that is connectedto the downstream conduit 35. The diaphragm 77 and a spring 79 normallykeep the inlet 76 open,

except when the pressure at the port 78 is large enough to overcome thepressure of the spring 79 and the pressure on the other side of thediaphragm 77 in the chamber 80. The diaphragm 77 divides the valve 50into chambers 80 and 81, and a bleed line 82 leads by a port 83 in thechamber 80 to an adjustable needle valve 62, which is used to set theratio in the timing operation, as will be described subsequently.

During inspiration, gas from the downstream conduit 35 flows through thecheck valve 48, and the restricted orifice 75 into the chamber 65 andbuilds up pressure there, for the inlet 76 is then shut off by the fullpressure of the downstream conduit 35 acting through the inlet 78 on thediaphragm 77. The orifice 75 is small, but as pressure builds up andbecomes great enough, it closes the closure member 70 against the port71 and disconnects the command signal conduit 43 from the main gassupply conduit 20.

When the inspiratory phase ends and expiration begins, the downstreamconduit 35 and the command signal conduit 43 are back bled to theatmosphere (how will be explained below), and then the inlet 76 isopened and the chamber 65 is bled slowly to atmosphere at a controlledrate through the needle valve 62. Backflow from the chamber 65 to thedownstream conduit is prevented by the check valve 48. Depending on theamount of gas in the chamber 65 which depends on the duration of theinspiratory phase the time for the chamber 65 to drop to a predeterminedpressure will vary. At that pressure, the closure member 70 is opened,and gas flows via the chamber 63 from the main gas supply conduit intothe command signal conduit 43. The command signal conduit 43 then raisesthe pressure in the chamber 40 of the main valve 30 and opens the inlet31 to start a new inspiratory phase.

While different values can be used, the springs may be set to close offthe port 71 when the pressure in the chamber 65 is about 7 psig. Theorifice 75 may be set so that in the maximum time for inspiration, thepressure in the chamber 65 will reach about 35 psig.

THE INITIATOR OR SENSITIVITY CONTROL 90 (FIGS. 1B and 6) The commandsignal conduit 43 is also connected by a branch to an initiator orsensitivity control device 90. This initiator 90 is used in thepressure-cycled mode to initiate the inspiratory phase, by overridingthe automatic ratio expiratory timer 60, which thus performs a backupfunction. The patients own termination of his expiratory phase is usedto trigger the passing of gas from the main gas supply conduit 20 intothe command signal conduit 43, thereby actuating the main valve 30. Theinitiator 90 may also be used in the volume-cycled mode, if desired,though normally it is not so used. In fact, if desired the volume port22 of the valve 17 may simply be shut off.

The initiator 90 has three chambers 91, 92, and 93 provided by a housing94, a diaphragm 95, and a rigid partition 96, as shown in a preferredembodiment in FIG. 6. The chamber 92 between the diaphragm 95 and therigid partition 96 is kept at atmospheric pressure by an atmosphericbleed port 97. The chamber 93 between the rigid partition 96 and thehousing 94 is provided with an inlet 98 that is connected to ordisconnected from a port 104 by a closure member 100 which is connectedto and is actuated by the diaphragm 95. An adjustable spring 101 exertspressure on the diaphragm 95, urging the closure member 100 toward aposition disconnecting the inlet 98 from the port 104. This inlet port98 is connected by a conduit 102 and the pressure port 23 of the valve17 to the main gas supply conduit 20. It may also, through an on-offvalve 103, be connected to the volume port 22 of the valve 17, so thatthe volume-cycled mode may or may not use the sensitivity control device90, whereas the pressure-cycled mode always uses this device 90. Thecommand signal conduit 43 is connected to the chamber 93 by a port 104.There is also a very important port 105 for the chamber 91, discussed inthe next section.

In the preferred structure shown in FIG. 6, the diaphragm 95 has abracket 99 secured thereto in engagement with a rod or shaft 106. AnO-ring 109 provides both a seal where the rod 106 passes through thepartition 96 and a pivot for it to swing about. The closure member 100comprises a disc threaded adjustably to the shaft 106 and provided withan annular gasket 108, effective in all rotational positions of the discto close the outlet port 104 except when the diaphragm 95 causes the rod106 to tilt and pivot on the O-ring 107. The spring 101 is of the leaftype with a right-angle portion 109 attached to the rod 106, in a way toenable some relative movement, such as sliding. A screw 87 enablesadjustment of the spring pressure, thereby setting the pressurerequested for the diaphragm 95 to open or close the port 104. There is astop 88 for the shaft 106 and a set-screw 89 for the disc-valve 100. Thespring 101 can be adjusted to set the patient-actuated pressure over therange between about 1 centimeter of water and 15 centimeters of water.

THE FACE MASK 110 AND THE AIRWAY CONDUIT 113 (FIGS. 1A and 1B) Thepatient typically wears a face mask 110 (FIG. 1A), which is connected bya conduit 111 to an exhalation valve 112. From the exhalation valve 112,a conduit 113 at airway pressure is connected (FIG. IE) to thesensitivity control device 90 at the port 105 on the opposite side ofthe diaphragm 95 from the central chamber 92 and on the same side as thespring 101. When the pressure in the airway 113 drops, the diaphragm 95is moved by the pressure of the spring 101, to tilt the rod 106 and openthe port 104, as will be seen subsequently in the explanation of theoperation of the ventilator.

THE PRESSURE SAFETY VALVE (FIG. 1B)

The airway conduit 113 is also connected to an inlet 119 of a pressure 5safety valve 120 leading in between two diaphragms 121 and 122 thatdivide the valve 120 into chambers 123, 124, and 125. The idea here isto prevent the buildup of any dangerous pressure in the lungs. Theeffective area of the diaphragm 121 is larger than that of the diaphragm122. On the opposite side of the larger diaphragm 121 is a spring 126,and (like the structure of the main valve 30) the smaller diaphragm 122and the larger diaphragm 121 are both connected to a valve closuremember 127 which closes an inlet 128 that is connected to the commandsignal conduit 43. When the port 128 is open the command signal can flowto atmospheric pressure through the chamber 125 a bleed port 129. Thechamber 123 is also bled to atmospheric pressure. If the pressure in theairway 113 becomes excessive (i.e., rises above a predeterminedpressure, such as 70 centimeters water, set as a limit by the spring126), it acts on the diaphragm 121, overcomes the pressure of the spring126 and opens the inlet 128, bleeding the command signal conduit 43 toatmosphere and thereby terminating the inspiratory phase.

THE PRESSURE CONTROLLER 130 (FIG. 18 AND 7) Normally, however, theinspiratory phase in the pressurecycled mode is terminated by a pressurecontroller 130. If the sigh function is to be omitted, the pressurecontroller may be built just like the pressure safety valve 120, but setfor lighter pressure to provide the normal pressure control for theventilator. When the sigh function (see below, re FIG. 1C) isincorporated, a preferred embodiment of the pressure controller 130 maybe as shown in FIG. 7. This unit 130 has a diaphragm 131 of largereffective area than either diaphragm 132 or diaphragm 133, between whichit lies, and these diaphragms 131, 132, and 133 cooperate with a housing114 to provide chambers 115, 116, 117, and 118, a spring 134 being inthe atmospheric chamber 118. The diaphragms 131 and 132 and 133 aresecured together and to a closure member 135 and normally urge itagainst an inlet port l36,which joins the end chamber 115 to the commandsignal conduit 43. When the closure member 135 is moved away from theport 136, the command signal conduit 43 is bled to atmosphere through aport 137. The chamber 117 between the two diaphragms 131 and 133 has aport 140 connected by a conduit 141 to the pressure outlet 25 from thevalve 18, and thereby, to the airway 113. The spring 134 is adjusted bya handle or shaft 142 to give a desired pressure on the closure member135. A guide pin 143 engages a groove 143a in a nut 143b to guide thenut 143b without rotation when the shaft 142 is turned. Since the valve18 has its inlet 24 connected to the airway pressure conduit 113, whenand only when the valve assembly 12 is in the pressure-cycled mode, theairway pressure is then conducted to the central chamber 116 of thepressure controller 130. The chamber 117, which lies between thediaphagms 131 and 133 is connected by a port 138 to a conduit 139leading to the sigh device 300.

Omitting for the present the effect of the sigh apparatus 300, the mainfunction of the pressure controller 130 is to terminate the inspiratoryphase when the pressure in the airway 113 reaches a predeterminedpressure. At this pressure, since the pressure in the airway 113 is alsothe pressure in the line 141 and in the chamber 116 during thepressure-cycled mode, the pressure in the chamber 116 and the pressureof the spring 134 are overbalanced, and the command signal line is bledto atmospheric pressure through the inlet 136, chamber 115, and port137. The command signal conduit 43 bleeds away the pressure in thechamber 40 of the main valve 30, and the port 31 is therefore closed.The operating point of the pressure controller can be set over a rangeof about to 50 cm water.

THE AIR SWITCH 145 AND PROFILE FLOW CONTROLLER 150 (FIG. 1A)

In the pressure-cycled mode, the valve 19 is used to connect thedownstream pressure conduit 35 leading from the main valve 30 to aconduit 144 leading to an air switch 145 (FIGS. 1A and 2). The airswitch 145 is a manually operated valve which sends the oxygen from theconduit 144 through a flowrate controller 150 to provide a controlledflow of the pure oxygen or sends it through a venturi 149, at which airis picked up to dilute the oxygen. It determines whether the patientgets 100 percent oxygen (if that is the gas supplied at the supply orone of various dilutions thereof.

Thus, the air switch 145 in one position connects the conduit 144 to aconduit 146 leading to a variable needle valve 147 and thereby through arestrictor orifice 148 to the venturi 149, and thence to the airwayconduit 113 to send oxygen-enriched air to the mask 110 therethrough.

In its other position, the air switch 145 connects the conduit 144 to aconduit 151 which leads to the profile flow controller 150, comprising avalve unit 152 with three chambers 153, 154, and 155. Two of thechambers 153 and 154 are divided from each other by a diaphragm 156 witha spring 157 in the chamber 153. The chamber 153 is kept at atmosphericpres sure through a bleed port 158. The third chamber 155 is dividedfrom the central chamber 154 by a poppet valve 160 and opening 161. Thepoppet valve 160 is normally urged into the opening 161 to close it by aspring 162 and is also actuated by the diaphragm 156. An inlet conduit163 into the third chamber is connected to the conduit 151 by a conduit159 and conducts oxygen into the central chamber 154 when the poppetvalve is open, at a rate determined by the amount by which the poppetvalve 160 is open. The gas may then pass through an outlet pon 164 andfrom thence to the airway pressure conduit 113. A by-pass is providedthrough a conduit 165 and a needle valve 166 to give a much smaller flowrate of gas from the conduit 151 to an inlet port 167 into the centralchamber 154. This is the terminal or minimum flow.

A pressure relief valve 168 may be incorporated to bleed the airway 113to atmosphere if the pressure introduced from the port 154 should becomeexcessive.

The pressure flow controller 150 sends gas to the patient at aregulatable large initial amount and at a flow rate that graduallyreduces toward or to a set minimum rate. The pattern of reduction, therate at which the flow rate decreases, is determined by the pressure onthe spring 157, which is adjustable to the patients requirements or tothe prescribed treatment. The maximum or initial flow rate is set by thespring 157, and the minimum or terminal flow is set by the needle valve166. Typically, the terminal flow is adjustable in the range of l to 10liters per minute, and the peak flow is adjustable in the range of 60 to100 liters per minute.

THE NEBULIZER 170 (FIG. 1A)

Preferably, the downstream conduit 35 is also connected to a nebulizer170 (FIG. 1A) through a restricted valve 171 to give a small flow ofhigh-pressure gas to atomize the liquid added to the main flow into theairway pressure conduit 113. Also, a pressure gauge 172 (FIGS. 1A and 2)may be connected to the airway pressure conduit 113 to give a reading ofairway pressure.

THE NEGATIVE PRESSURE DEVICE AND THE EXHALATION VALVE 112(FIG.1A),

WITH ITS ASSOCIATED PRESSURE RELIEF VALVE 200 (FIG, 1B)

The negative pressure device 55, when used, connects the chamber 57 by aport 174 to a conduit 175 through an adjustable needle valve 176 (withcontrol 176a in FIG. 2) and into the exhalation valve 112 at an inlet177. A closure member 178 in the negative pressure device 55 isconnected to the diaphragm 58, and the diaphragm 58 and a spring 179normally keep the port 174 closed.

The negative pressure port 177 of the valve 112 leads into a venturi 180in a chamber 181, into which the conduit 111 and 113 also open throughports 182 and 183; the flow from the venturi 180 passes to an outletvalve 184, the outlet port 185 of which is normally kept closed by thepressure of a spring 186 (or similar device, such as a bladder) oninterconnected diaphragms 187 and 188, and by the pressure from aconduit 190. This conduit 190 is connected by a restrictor orifice191(FIG. 113) to the airway pressure conduit 113. The conduit 190 is asmall-diameter line so that it is very responsive, and the action willbe described later. This line 190 and its restrictor conduit 191 areconnected by an inlet 192 into a chamber 194 ofthe valve 112.

The line 190 is also connected to a pressure relief valve 200 at aninlet 201 (FIG. 1B). The pressure relief valve 200 has a singlediaphragm 202 dividing the valve 200 into a chamber 203 having a port204 to atmosphere on one side, and a chamber 205 having a port 206connected to the downstream conduit 35. A spring 207 aids the diaphragm202 in keeping the port 201 open, and when it is open, the auxiliaryline 190 is bled to atmosphere.

THE PRESSURE RELIEF VALVE 51 (FIG. 1A)

The conduit 43 also leads to the pressure relief valve 51 (FIG. 1A),which is a secondary valve for the main valve 30 and is used in bothmodes. The valve 51 has a single diaphragm 195 with a chamber 196 on oneside connected by a port 197 to the command signal conduit 43. A valve198 connected to the diaphragm 195 is in the other chamber 199 andnormally acts to close an inlet port 207a connected to the downstreamconduit 35. A bleed port 208 to atmosphere is provided from the chamber199, and a spring 209 tends to help open the valve 198.

The pressure relief valve 51 is closed so long as there is apredetermined amount of pressure in the command signal conduit 43;otherwise it is open. When the valve 51 is closed, the pressure in thedownstream conduit 35 is monitored; when the valve 51 is opened, thedownstream conduit 35 is bled to atmospheric. Thus, when the commandsignal conduit 43 has enough pressure to open the main valve 30, thesame pressure closes the relief valve 51. And when the command signalconduit 43 is bled to atmosphere through either the pressure controller130 or through the pressure safety valve 120, at the end of theinspiratory phase, the valve 51 is opened and the downstream conduit 35is at once bled to the atmosphere.

THE MANUAL TRIGGER VALVE 210 (FIG. 1B)

For manual operation in both modes there is provided a manual triggervalve 210 (FIG. 18) comprising a valve body 211 having an inlet 212connected to the internal supply conduit 20 and having a valve 213normally urged by a spring 214 to a closed position at a port 215. Whenthe valve 213 is opened by depressing a manual stem 219, the air canflow from the conduit 20 through the trigger valve 210 from the chamber216 to the other chamber 217 and thence by a port 218 to the commandsignal conduit 43, whence it flows to the chamber 40 and opens the valve40. Thus the valve 210 ena bles the physician manually to monitor theventilator, to initiate the inspiratory phase.

All of the parts so far described are used in the pressure-cycled modeof operation, and some of them are also used in the volume-cycled modeof operation. The ones next to be described are used only in thevolume-cycled mode.

VOLUME MODE: VOLUME PROFILE REGULATOR 22 (FIGS. 1A AND 8) i As stated,in the volume-cycled mode of operation the sensitivity control 90 may ormay not be used, depending on whether the valve 103 is open or closed.In either event, however, the valve 19 (FIG. 1B) is set so'that thedownstream gas flows from the conduit 35 into a conduit 220 leading bytwo branch conduits 221 and 222 to a volume profile regulator 225 and aninspiratory time regulator 240.

The volume profile regulator 225 is used to enable the flow to thepatient in this mode to start at a large initial flow and then todecrease as the inspiratory phase continues until the end of the cycle.In this respect it resembles but is difi'erent from the pressure flowcontroller 150.

The volume profile regulator 225 (see especially FIG. 8) comprises ahousing 226 having a larger area diaphragm 227, a smaller-area diaphragm228, and a rigid partition 229. One side of the diaphragm 227 is open tothe atmosphere, as by a port 2260 in the housing 226. A poppet valve 230is urged by the diaphragms 227 and 228 and springs 231 and 231a toward aposition away from an opening 232 which the poppet valve 230 sometimescloses. Gas from the conduit 221 enters by an inlet port 224 into achamber 233 and goes through the opening 232 controlled by the poppetvalve 230 to a chamber 234, and from thence by an outlet 235 to aconduit 236 leading to a control valve 237 and thence to the airwaypressure conduit 113. The control valve 237 with indicator 237a in FIG.2, enables adjustment of the volume in a manner subsequently to beexplained. The control valve 237 is an integral part of a timevolumecontrol unit 275 which is given more attention below.

The volume profile flow regulator 225 also has a chamber 238 between thediaphragm 227 and 228 with a port 239. As will be seen, during theinspiratory phase, pressure builds up in the chamber 238 and graduallyreduces the flow out through the port 235 by moving the poppet valve 230toward the opening 232. The pressures of the springs 231 and 231a, thestiffness of the diaphragms 227 and 228, and their areas relative toeach other, cooperate with the variable pressure of gas into the chamber238 to determine the profile of the inspiratory phase.

THE INSPIRATORY TIMER 250 AND ASSOCIATED ELEMENTS (FIGS. 1A)

The oxygen from the conduit 222 enters the inspiratory time regulator240 through a flow-reducing restricted orifice 241 and an inlet port242. The purpose of the inspiratory time regulator is to provide asupply of gas at a regulated pressure to the inspiratory timer 250. Adiaphragm 243 is loaded by a spring 242 to close off a vent port 248 toatmosphere. The gas entering the inlet port 242 flows to an outlet port245 via an annular chamber 249, except for gas that is vented toatmosphere from the chamber 249 by the vent port 248. This ventingserves to keep the gas supplied to the outlet port 246 at a constantpressure, for as the pressure increases in the chamber 249, thediaphragm 243 is moved up to increase the bleed flow through the ventport 248; since a small motion of the diaphragm 243 will create a largechange in bleed flow, the pressure will remain practically constant.

The regulator 240 is set to deliver to the outlet port 245 and a conduit246 regulated pressure at a desired level, and the conduit 246 isconnected through a needle valve 247 to an inspiratory timer 250, withindicator 250a of FIG. 2. The needle valves 247 and 237 are interactingand form part of the timevolume control device 275 discussed below, bywhich the inspiratory volume and time can be changed.

The outlet from the needle valve 247 leads to a port 251 in afixed-capacity center chamber 252 of the inspiratory timer 250 betweentwo diaphragms 253 and 254, a larger diaphragm 253 and a smallerdiaphragm 254. To both diaphragms 253 and 254 is connected the stem 255of a closure valve 256 for an inlet 257 which is connected to thecommand signal conduit 43 and normally holds that inlet 257 closed. Fromthe chamber 258 with the inlet 257 is a bleed 259 to atmosphere, and thespring chamber 260 of the larger diaphragm 253 also has a bleed port 261to atmosphere, as well as a spring 262 bearing on the diaphragm 253.

Thus, the gas that passes through the pressure regulator 240 and thecontrol valve 247 gradually builds up pressure in the timer 260 duringthe inspiratory phase, starting from atmospheric pressure at thebeginning of each inspiratory phase. When a predetermined time haselapsed, the pressure in the chamber 252 reaches a predetermined levelthat opens the closure member 256, uncovering the inlet port 257. Asthis inlet port 257 is uncovered, the rush of pressure of the gasflowing in from the command signal conduit 43 helps to snap open thevalve, and the command signal conduit 43 is quickly bled to atmosphere,ending the inspiratory phase by resulting in closure of the main valve30.

In order to prepare the inspiratory timer 250 for the next phase, bybleeding the pressure in the chamber 252 to atmospheric, the inspiratorytimer 250 is connected by conduits 263 and 264 to another pressurerelief valve 265 at an inlet 266. The pressure relief valve 265 has asingle diaphragm 267 with a spring 268 in one chamber 269, urging avalve closure member 270 normally to open the inlet 266. The chamber 269is bled to atmosphere by a port 271 so that when the valve 270 is inopen position, the gas from the conduit 263 is vented to the atmosphere.A chamber 272 on the other side of the diaphragm 267 is connected by aport 273 to the downstream air conduit 35.

Thus, when the inspiratory timer ends the inspiratory cycle by bleedingthe command signal conduit 43 to atmosphere, the drop in pressure in theconduit 43 opens the valve 51 and the downstream conduit 35 is bled toatmosphere. The resultant reduction in pressure of the conduit 35enables the spring 268 to open the closure member 270 away from theinlet port 266, and the conduit 263 and the chamber 252 are bled toatmosphere. The valve 256 is then closed by the spring 262. When thenext inspiratory phase begins, the surge of pressure in the downstreamconduit 35 closes the valve 265, and the flow of gas through the needlevalve 247 can build up pressure in the chamber 252.

The diaphragms 253 and 254 and the bias spring 262 are sized so that thevalve seat 256 is closed when the pressure in the intermediate chamber252 is atmospheric and opens when the pressure reaches a nominal valueof 5 psig (at the end of the inspiratory phase), the pressure beingcreated by the flow of supply gas through the needle valve 247 into thefixed capacity chamber 252. The time that it takes to build up thepressure, say, of 5 psi, represents the inspiratory time. It may beadjusted from 0.5 to 4 seconds by setting the needle valve opening 247.At the end of the inspiratory phase, the pressure is returned toatmospheric by the action of the pressure release valve 265.

The pressure increase from to 5 psig is proportional to the total volumewhich passes through the needle valve 247. This volume is proportionalto area .r time. The total volume being a constant in the calibration,the valve opening is therefore proportional to the reciprocal of time;hence, the non-linearity of the time scale graduation.

The inspiratory timer 250 is also connected by the conduit 263 and theport 239 to the chamber 238 of the volume profile regulator 225 whichlies in between the two diaphragms 227 and 228. Thus, during theinspiratory phase, the pressure builds up there and gradually moves thepoppet valve 230 closer to its opening 232, shaping the fiow profile ofthe inspiratory phase.

As the pressure in the chamber 238 increases, it creates a forceopposing the force of the spring 231, and the regulator setting isdecreased. As a result, the output pressure of the regulator decreasesprogressively as the pressure in the chamber 238 increases. Typically,the output pressure goes from 30 psig to 5 psig as the inspiratory timerpressure goes from O to 5 psig.

THE VOLUME-TIME CONTROLLER 275 (FIGS. 1A and 9-13) A housing 276 isprovided with an inlet 277 and an outlet port 278. A variable areaopening is created by moving a slot 280 (preferably rectangular in crosssection) of an adjustable sleeve 281 relative to a slot 283 in thestationary housing 276, the slot 283 also being preferably rectangularin cross section. A maximum size of opening is obtained when the twoopenings 280 and 283 coincide (FIG. 12C). Reduction from that maximumcondition is done in two modes: a rotation and an axial displacementofthe adjustable sleeve 281.

The rotation of the sleeve 281 is directly related to the volume setting(V); the axial displacement is proportional to the reciprocal ofinspiratory time (Hi). The net area of the opening in then proportionalto: Volume (l/Time). Since the flowrate is directly proportional to thearea, we have:

Flowrate Volume x l/time) or the fundamental relationship:

Volume Flowrate x time.

The settings of volume and inspiratory time are thus independent andnoninteracting. A change in volume setting modifies the opening area,and therefore the flowrate, in a direct relationship. A change in theinspiratory time setting modifies the opening area in an inverse ratio;an increase in time decreases the flowrate, in order to maintain thesame total volume in a longer time.

The axial movement of the sleeve 281 is the axial displacement of ascrew 284 actuated directly, by an inspiratory time knob 285, the sleeve281 being spring loaded by a spring 286 against the screw 284 to assurecooperation between the screw 284 and the sleeve 28]. The knob 285drives, through a step-up gear train 287, 288 the needle valve 247 ofthe inspiratory timer. The rotation of the sleeve 28] is obtained by agear train 290, 291, in which the driven gear segment 291 is attached tothe sleeve shaft 292 (FIG. 10), and the driving gear 290 is actuated bya volume knob 237 a (FIGS. 2 and 10).

FIGS. 12A through 12D show four extreme positions of the two orifices280 and 283:

FIG. 12A shows the small overlap in area of the rectangular orifices 280and 283 when the time shaft is in its full clockwise position to givethe maximum time interval, while the volume shaft is in its fullcounterclockwise position to give minimum volume. The orifices 280 and283 are in different planes and at minimum overlap in both directions.FIG. 128 shows the larger overlap, with both orifices on the same planebut at extreme opposite angles. This setting gives both minimum time andminimum volume, for both the time shaft and the volume shaft are intheir full counterclockwise positions.

In FIG. 12C, the maximum volume is obtained, with the orifices 280 and283 coinciding, while the time is again at minimum. The time shaft isfully counterclockwise, while the volume shaft is fully clockwise.

In FIG. 12D the volume shaft is again fully clockwise to give maximumvolume, while maximum time is also obtained by having the time shaftfully clockwise.

In a typical instance, the area of the full overlapi.e., the area ofeach of the orifices 280 and 283, is 0.01 square inch (FIG. 12C). InFIGS. 12B and 12D, the area of overlap is then 0.001 square inch, and inFIG. 12A the area of the overlap is only 0.0001 square inch.

INTERRELATIONSI-IIPS AND GENERAL FUNCTIONING OF THE ASSEMBLY (FIGS. 1AAND 13) Now that the elements other than the sigh device 300 have beendescribed and their individual operation indicated, some generalrelationships and functioning will be noted before the detailedoperation is given.

As noted earlier, the selector valve assembly 12 has three positions:pressure-cycled, volume-cycled" and off." In the off position, theregulated gas supply 10 is shut off from the entire device. In thepressure-cycled position, (1) The internal supply conduit 20 to the mainvalve 30 is connected to the regulated gas supply 10, (2) The downstreamconduit 35 leading from the main valve 30 is connected to the air switch145. (3) The connecting line 141 between the patient supply line orairway conduit 113 and the pressure controller 130 is open. (4) Thesupply line 102 between the internal supply conduit 20 and the initiatoris open. In the volumecycled position, (1) The internal supply conduit20 to the main valve 30 is connected to the regulated gas supply 10, and(2) The downstream conduit 35 leading from the main valve 30 to thevolume control unit 275 is open.

The two-position main valve 30 is either fully open or fully closed,depending on the command signal from the conduit 43. If the commandsignal, i.e., the pressure in the conduit 43 increases beyond apredetermined value, such as 20 psig, the main valve 30 opens andremains open. If the signal decreases to a lower predetermined value(such as approximately 10 psig), the main valve 30 closes.

The relief valve 51 exhausts the downstream pressure in the conduit 35to atmosphere when the main valve 30 closes.

On a command signal from the airway conduit 113, typically a slightvacuum, the initiator 90 sends high-pressure gas from the conduits 20and 102 to the command signal conduit 43, causing the main valve 30 toopen. The reader will recall that the initiator 90 has a diaphragm thatis subjected to a differential pressure; atmospheric pressure on oneside in the chamber 92 and, at this time, a slight vacuum on the otherside in the chamber 91 generated by the patient and sent there by theairway conduit 113. The effort created by the differential pressureopens the valve closure in the compartment 93, and the port 104 thensupplies the high-pressure gas from the conduit 102 to the commandsignal conduit 43. The magnitude of the vacuum required to generate thecontrol signal is adjustable by the loading spring 101.

The pressure controller 130 also senses the pressure in the airwayconduit 1 13, with a desired set pressure, and when the two becomeequal, generates a signal to shut off the main valve 30, by bleeding thecommand signal conduit 43 to atmosphere.

The airway pressure, which is the patients breathing pressure, starts atatmospheric pressure or at a slight vacuum at the beginning of eachinspiration,then gradually increases during the inspiratory period tothe preset value; this may be a value from a minimum of 5 cm. water to amaximum about 60 cm. water. When the pressure in the airway conduit 113has reached the preset value, the gas in the command signal conduit isexhausted to atmosphere, causing a pressure drop, which, in turn causesthe main valve 30 to close, shutting off the gas supply to the patient.

The pressure safety valve 120 also senses the airway pressure, comparesit with a preset maximum (approximately 70 cm. water) pressure. If thepressure in the airway conduit 113 exceeds the preset maximum pressure,a signal is generated to shut off the main valve 30, by exhausting thecommand signal conduit 43 to atmosphere. Again, this pressure dropcauses the main valve 30 to close.

When a desired expiratory time has elapsed, the expiratory timer 60initiates a new inspiratory phase by connecting the high-pressure gassupply conduit to the command signal conduit 43, which opens the mainvalve 30. During the inspiratory phase, the expiratory timer 60 isrecharged. The intensity or pressure of the recharge is directlyproportional to the inspiratory time. At the end of the inspiratoryphase and the beginning of the expiratory phase, the expiratory timer 60starts discharging (bleeding off air pressure) at a preset rate. Whenthe discharge reaches a reference low level, a new inspiratory phase isinitiated. If the rate of discharge is set at a value such that thedischarge time is twice as long as the recharge time, the respirator isknown to operate on a l:2 inspiratory/expiratory ratio. This ratio ismaintained even though the inspiratory time varies from one breath toanother. The automatic ratio expiratory timer 60 is effective in bothpressure-cycled and volume-cycled modes.

The air switch 145 is connected to the downstream side of the main valve30 by the conduits 35 and 144. If is effective in the pressure-cycledmode only, when it provides a selection of delivering pure oxygenthrough the profile flow controller 150 or an oxygen-air mixture throughthe venturi 149.

The flow controller 150 provides the patient with a suitable flowpattern during the inspiratory period. The demand of gas is greatest atthe start of the inspiratory phase; then it gradually diminishes. Theflow controller operates on the basis of creating a variable orifice160, 161 as a function of the difference between a spring-set pressureand the patients airway pressure. The flow is then determined by thearea of the orifice. By adjusting manually the magnitude of thedifferential pressure, a higher or lower flow rate can be obtained. Amanual setting limits the maximum opening of the variable orifice 160,161. The initial high flow, corresponding to this maximum opening,constitutes the peak flow, and the manual setting is the flow ratecontrol. An adjustable by-pass flow through the valve 166 provides aterminal flow control.

ln the alternate position of the selector switch 145, the profilefunction is by-passed, and the gas supply is applied to the nozzle ofthe venturi 149. The flow from the nozzle draws in air, producing anair-gas mixture. The flow rate is then controlled by the needle valve147, which is actuated by the control knob of the profile flowcontroller 150, thus providing a single common control knob for bothoperations.

The manual trigger 210 enables manual initiation of the ventilator intoan inspiratory phase by connecting the gas supply conduit 20 to thecommand signal conduit 43, thus causing the main valve 30 to open.

A slight vacuum created at the exhalation valve 112 by the ventilatorduring the expiratory phase known as "negative pressure," (see U. S.Pats. Nos. 3,191,596 and 3,265,06l The driving gas supplied from the gassupply conduit 20 upstream of the main valve 30 passes through thepneumatically controlled valve 55 and then through the adjustable needlevalve 176 to the venturi 180 located in the exhalation valve 112. Thecontrol valve 55 is actuated by the pressure from the downstream side ofthe main valve 30 by the conduit 35. The needle valve 176 enablesadjustment of the value of the negative pressure.

The volume control is obtained by the volume selector 275, theinspiratory timer 250, and the volume profile regulator 225.

The volume selector 275 enables selection of a desired volume to bedelivered, by setting a dial. The dial may be graduated in volume unitsor have reference marks. The input of the unit is connected to thedownstream conduit 236 from the volume profile regulator 225. The outputof the unit is connected to the patients breathing circuit.

The inspiratory timer 250 controls the time that it takes to deliver theselected volume. The supply pressure for the timer 250 is regulated toan intermediate value (e.g., approximately 25 psig) to minimize theeffect of pressure variations in the main supply line 20. The gas isthen metered through a needle valve 247 into the fixed-capacity chamber252, where the pressure increases as a function of time. When thepressure reaches a reference value (e.g., 5 psig), the timer 250exhausts the command signal conduit 43 to atmosphere which, in turn,shuts off the main valve 30 and the gas supply to the patient. Its dialmay be graduated in seconds or have other reference marks.

The actions of the volume selector 275 and the inspiratory timer 250 arecombined in such a way that the settings of the volume and theinspiratory time are noninteracting. Changing the volume setting doesnot affect the time setting; similarly, changing the inspiratory timedoes not affect the volume settmg.

The volume profile regulator 225 supplies the gas to the volume selector275. It regulates the gas pressure to a maximum of, e.g., 30 psig, atthe beginning of the inspiratory period and gradually reduces it to aminimum of, e.g., 5 psig at the end of the period. As a direct result ofthe variable pressure, the flow rate is reduced accordingly, providing acontrolled pattern.

The decrease in the regulated pressure is synchronized with the controlpressure of the inspiratory timer 250. This provides a reproducible flowpattern independently of the inspiratory time setting.

The pressure release valve 51 is open to atmosphere when the pressure inthe command signal conduit 43 is low (near atmospheric). During theinspiratory phase, this pressure is high, and it closes the port 207a.At the end of the inspiratory phase and the start of the expiratoryphase, the pressure in the conduit 43 is bled to atmospheric, causingthe pressure release valve 51 to open and bleed the downstream conduit35 to atmosphere.

The exhalation valve 1 12 provides the means of opening the patientsairway to atmosphere during the expiratory period, and conversely ofclosing the communication with atmosphere during the inspiratory period.A plastic bladder or diaphragm 187 works in cooperation with theexhalation port to control the opening. When the bladder is inflated,(or the diaphragm 187 is under pressure) there is no communication withatmosphere. When it is deflated, the communication is established. Theoperation of the bladder or diaphragm 187 is automatically controlled bythe ventilator through the auxiliary line 190.

OPERATION: PRESSURE-CYCLED MODE The pressure-cycle mode of operationwill be described first in its use as an assist type of ventilator, withthe patient supply-

1. A ventilator for providing breathing gas to a patient during aninspiratory phase and letting him exhale during an expiratory phase,including in combination: a gas supply conduit for supplying abreathable gas under pressure, a downstream conduit, a command signalconduit, an airway conduit suitable for connection to a patient, meansconnecting said downstream conduit to said airway conduit, main valvemeans connected to said command signal conduit for connecting said gassupply conduit to said downstream conduit during each said inspiratoryphase when the pressure in said command signal conduit rises above afirst predetermined pressure level, and for closing off said downstreamconduit from said gas supply conduit during each said expiratory phasewhen the pressure in said command signal conduit drops below a second,lower, predetermined pressure level, phase-actuation means connected tosaid command signal conduit for terminating each said inspiratory phaseand commencing a said expiratory phase, by bleeding said command signalconduit to atmosphere, means connected to said command signal conduitfor bleeding said downstream conduit to atmosphere when said commandsignal conduit pressure drops below said second predetermined pressurelevel at the commencement of said expiratory phase, ratio meansconnected to said command signal conduit, said downstream conduit andsaid gas supply conduit for ending the expiratory phase and initiating anew inspiratory phase by increasing the pressure in said command signalconduit above said first predetermined pressure level by supplying gasfrom said gas supply conduit to said command signal conduit, after alapse of time following the commencement of said expiratory phase, saidratio means having means for sensing the duration of each inspiratoryphase and for establishing a maximum duration of the succeedingexpiratory phase as a time ratio of the inspiratory phase to the nextsucceeding expiratory phase, and means for varying the setting of saidtime ratio.
 2. The ventilator of claim 1 wherein said phase-actuationmeans is connected to said airway conduit and is actuated by thepressure in said airway conduit reaching a third predetermined pressurelevel.
 3. The ventilator of claim 2 having sensitivity control meansconnected to said airway conduit for connecting said gas supply conduitto said command signal conduit and thereby to raise the pressure thereinabove said first predetermined pressure level when the pressure in saidairway conduit drops below a fourth predetermined pressure level, due tothe commencement by the patient of an inspiratory phase, and to closeoff said command signal conduit from said gas supply conduit when thepressure in said airway conduit rises above said fourth predeterminedpressure level, said sensitivity control means thereby overriding saidratio means whenever said patient initiates an inspiratory phase beforethe time lapse following commencement of an expiratory phase has not yetreached the time at which said ratio means would have acted to initiatea said inspiratory phase.
 4. The ventilator of claim 2 wherein saidmeans for connecting said downstream conduit to said airway conduitcomprises means for adjusting the pattern of the flow of gas from aninitial peak flow through a gradually decreasing flow to a minimalterminal flow, including means for varying the initial peak flowindependently of said minimal terminal flow.
 5. The ventilator of claim4 wherein said means for adjusting the pattern of flow of gas comprisesfirst flow means for providing a minimum constant flow from saiddownstream conduit to said airway conduit, second flow means forproviding an adjustable initial peak flow from said downstream conduitto said airway conduit, and means responsive to the pressure in saidairway conduit for continually reducing the flow through said secondflow means from said peak flow as the pressure in said aIrway conduitincreases.
 6. The ventilator of claim 5 wherein said first flow meansincludes means for adjusting the amount of said constant flow.
 7. Theventilator of claim 1 wherein the means for connecting said downstreamconduit to said airway conduit comprises means for determining thevolume of gas to pass from said downstream conduit into said airwayconduit during each inspiratory phase, means for determining the timeover which said volume is to be delivered, and means for actuating saidphase-actuation means at the conclusion of that said time.
 8. Theventilator of claim 7, wherein said means for determining the volumecomprises two relatively rotatable conduit means having alignableorifices, a first said conduit means being connected to said downstreamconduit and a second said conduit means being connected to said airwayconduit, and means for rotating said conduit means relative to eachother for varying the area of opening of the orifices that provide fluidconnection, said means for determining the time comprises means fordisplacing said conduit means axially relative to each other to vary thearea of opening of the orifices that provide fluid connection and flowvalve means connected to said downstream conduit, and sending gas tosaid means actuating said phase-actuation means.
 9. The ventilator ofclaim 8 wherein said downstream conduit is connected to said firstconduit means through a pressure regulator having an orifice regulatingthe passage of gas from said downstream conduit and pressure-controlmeans regulating the size of said orifice, said pressure control meansbeing connected to said flow valve means downstream thereof.
 10. Theventilator of claim 8 wherein said means actuating said phase-actuatingmeans comprises pressure-operated means for bleeding said command signalconduit when the amount of gas that has passed through said flow valvemeans raises the pressure exerted on said pressure-operated means to apredetermined value.
 11. The ventilator of claim 1 having manual valvemeans for passing gas directly from said gas supply conduit to saidcommand signal conduit, for manual initiation of an inspiratory phase.12. The ventilator of claim 1 wherein said main valve means comprises ahousing divided into chambers by first and second diaphragms, said firstdiaphragm being larger in effective area than said second diaphragm,said first diaphragm having one side open to the atmosphere, a firstchamber between said first and second diaphragms connected to saidcommand signal conduit, a second chamber bounded by said seconddiaphragm and having an inlet connected to said gas supply conduit andan outlet connected to said downstream conduit, valve means for openingand closing said inlet, said valve means being connected to both saidfirst and second diaphragms for movement with them, and spring meansurging said valve means normally to close said inlet, said valve meansopening said inlet when the pressure in said first chamber rises to saidfirst predetermined pressure level, said valve means, upon commencementof its opening by the pressure on said first diaphragm being rapidlyopened by the pressure of the gas entering said inlet from said gassupply conduit and acting on said second diaphragm, said valve meansthereafter preventing closure until the pressure on said first diaphragmdrops below said second pressure level, at which time said downstreamconduit is being bled by its said bleeding means, so that said valvemeans rapidly and positively closes against said inlet, due to thelowering of pressure in said second chamber able to act on said seconddiaphragm.
 13. The ventilator of claim 1 wherein said ratio meanscomprises a reservoir, a restricted orifice connecting said reservoir tosaid downstream conduit, so that pressure in said reservoir builds upgradually toward a value still somewhat less than that of saiddownstream conduit during the time that said main valve means connectssaid gas supply conduit to said downstream conduit, which is during theentire inspiratory phase, check valve means between said downstreamconduit and said reservoir, to prevent back flow from said reservoir tosaid downstream conduit when said downstream conduit is bled toatmosphere, means sensitive to the pressure in said reservoir foropening and closing off a connection between said gas supply conduit andsaid command signal conduit, said connection being closed off so long asthe pressure in said reservoir remains above a predetermined level, andbleed means actuated by the drop in pressure in said downstream conduitto atmospheric for bleeding said reservoir to atmosphere at apredetermined flow rate during said expiratory phase, the time for saidbleed means to cause the pressure in said reservoir to drop below thelevel where said command signal conduit is connected to said gas supplyconduit thereby depending on the length of duration of said inspiratoryphase, during which the pressure in said reservoir is continually builtup.
 14. The ventilator of claim 1 having switch means for causing, in afirst position, the inspiratory phase to terminate when the pressure insaid airway conduit reaches a certain level and for causing, in secondposition, the inspiratory phase to terminate after a given volume hasbeen delivered from said downstream conduit to said airway conduit. 15.A ventilator for pressure-controlled operation with an inspiratory phaseand an expiratory phase, including in combination: a gas supply conduitfor supplying a breathable gas under pressure, a downstream conduit, acommand signal conduit, an airway conduit suitable for connection to apatient, means connecting said downstream conduit to said airwayconduit, main valve means connected to said command signal conduit forconnecting said gas supply conduit to said downstream conduit duringeach said inspiratory phase when the pressure in said command signalconduit rises above a first predetermined pressure level and for closingoff said downstream conduit from said gas supply conduit during eachsaid expiratory phase when the pressure in said command signal conduitdrops below a second, lower, predetermined pressure level, sensitivitycontrol means connected to said airway conduit for connecting said gassupply conduit to said command signal conduit and thereby to raise thepressure therein above said first predetermined pressure level when thepressure in said airway conduit drops below a third predeterminedpressure level due to the commencement by a patient of an inspiratoryphase, and to close off said command signal conduit from said gas supplyconduit when the pressure in said airway conduit rises above said thirdpredetermined pressure level, means for bleeding said command signalconduit to atmosphere actuated by the pressure in said airway conduitreaching a fourth predetermined pressure level, as upon commencement ofan expiratory phase, means connected to said command signal conduit forbleeding said downstream conduit to atmosphere when said command signalconduit pressure drops below said second predetermined pressure level,as at the beginning of said expiratory phase, and ratio means connectedto said command signal conduit, said downstream conduit and said gassupply conduit for ending said expiratory phase and initiating a newinspiratory phase by increasing the pressure in said command signalconduit above said first predetermined pressure level by supplying gasfrom said gas supply conduit to said command signal conduit, if thepatient fails to initiate a new inspiratory phase for himself, after atime lapse following the commencement of a said expiratory phase, saidratio means having means for sensing the duration of each inspiratoryphase and for establishing automatically a maximum duration of thesucceeding expiratory phase as a time ratio of the inspiratorY phase tothe next succeeding expiratory phase.
 16. The ventilator of claim 15having manual valve means for passing gas directly from said gas supplyconduit to said command signal conduit, for manual initiation of aninspiratory phase.
 17. The ventilator of claim 15 wherein said means forconnecting said downstream conduit to said airway conduit comprises atwo-position valve having a first position wherein said downstreamconduit is connected to said airway conduit through means for adjustingflow, a restricted orifice, and a venturi in series, said venturi havingan air inlet from atmosphere and drawing in air therefrom to dilute saidgas to a desired dilution, said valve having a second position whereinthe connection is through means setting the pattern of the flow of gasfrom an initial peak flow and a gradually decreasing flow to a minimalterminal flow.
 18. The ventilator of claim 15 wherein said means forconnecting said downstream conduit to said airway conduit comprisesmeans for adjusting the pattern of the flow of gas from an initial peakflow and a gradually decreasing flow to a minimal terminal flow,including means for varying said initial peak flow independently of saidminimal terminal flow.
 19. The ventilator of claim 18 wherein said meansfor adjusting the pattern of flow of gas comprises: first flow means forproviding a minimum constant flow from said downstream conduit to saidairway conduit, second flow means for providing an adjustable initialpeak flow from said downstream conduit to said airway conduit, and meansresponsive to the pressure in said airway conduit for continuallyreducing the flow through said second flow means from said peak flow asthe pressure in said airway conduit increases.
 20. The ventilator ofclaim 19 wherein said first flow means includes means for varying theminimum constant flow.
 21. The ventilator of claim 18 wherein said meansfor adjusting the pattern of the flow of gas comprises a housing dividedby a diaphragm and a partition into first, second, and third chambers,said first chamber being open to the atmosphere and bounded by saiddiaphragm, said second chamber being between said diaphragm and saidpartition and having an inlet connected to said downstream conduitthrough an adjustable needle valve to deliver said minimal terminalflow, and an outlet connected to said airway conduit, said third chamberhaving an inlet connected directly to said downstream conduit, saidpartition having an opening therethrough connecting said second andthird chambers, valve means for opening and closing said opening andconnected to and controlled by said diaphragm, spring means in saidhousing for exerting pressure on said diaphragm, and compression meansconnected to said spring means for compressing said spring means forvarying its pressure on said diaphragm, the pressure in said airwayconduit and in said second chamber acting on said diaphragm and tendingto close said valve means.
 22. The ventilator of claim 15 wherein saidairway conduit includes an exhalation valve having a housing dividedinto three chambers by first and second diaphragms, so that there are afirst chamber bounded by said first diaphragm and having an inlet, asecond chamber between said diaphragms and open to the atmosphere, and athird chamber bounded by said second diaphragm and connected to saidairway conduit, first valve means opened and closed by said diaphragmsfor connecting said third chamber to the atmosphere, spring meansnormally urging said valve means toward a closed position, and anauxiliary conduit connected to said inlet and connected through anadjustable valve providing a variable-size restricted orifice to saidairway conduit.
 23. The ventilator of claim 22 provided with a pressurerelief valve having a housing divided by a diaphragm into two chambers,one connected to atmosphere and having an inlet connected to saidauxiliary Conduit, and the other connected to said downstream conduit,and valve means connected to said diaphragm for opening and closing saidinlet, with spring means normally urging said valve means to open saidinlet.
 24. The ventilator of claim 15 wherein said main valve meanscomprises a housing divided into chambers by first and seconddiaphragms, said first diaphragm being larger in effective area thansaid second diaphragm, said first diaphragm having one side open to theatmosphere, a first chamber between said first and second diaphragmsconnected to said command signal conduit, a second chamber bounded bysaid second diaphragm and having an inlet connected to said gas supplyconduit and an outlet connected to said downstream conduit, valve meansfor opening and closing said inlet, said valve means being connected toboth said first and second diaphragms for movement with them, and springmeans urging said valve means normally to close said inlet, said valvemeans opening said inlet when the pressure in said first chamber risesto said first predetermined pressure level, said valve means uponcommencement of its opening by the pressure on the larger said firstdiaphragm being rapidly opened by the pressure of the gas entering saidinlet from said gas supply conduit and acting on the smaller said seconddiaphragm, said valve means thereafter preventing closure until thepressure on said first diaphragm drops below said second pressure level,at which time said downstream conduit is being bled to atmosphere by itssaid bleeding means, so that said valve means rapidly and positivelycloses against said inlet, due to the lowering of pressure in saidsecond chamber able to act on said second diaphragm.
 25. The ventilatorof claim 15 wherein said sensitivity control means comprises a housingdivided into three chambers by a diaphragm and a partition, a firstchamber bounded by said diaphragm and connected to said airway conduit,a second chamber between said diaphragm and said partition and open tothe atmosphere, and a third chamber bounded by said partition and havingan inlet connected to said gas supply conduit and an outlet connected tosaid command signal conduit and valve means extending through saidpartition and sealed thereto and actuated by said diaphragm for openingand closing the connection between said inlet and said outlet and springmeans urging said valve means to close said connection between saidinlet and said outlet so that when said inlet is opened by creation of avacuum in said first chamber, gas from said gas supply conduit flowsinto said command signal conduit.
 26. The ventilator of claim 25 havingmeans for adjusting said spring pressure.
 27. The ventilator of claim 15wherein said ratio means comprises a reservoir connected by a restrictedorifice to said downstream conduit, so that pressure in said reservoirbuilds up gradually and continuously during the time when the pressurein said downstream conduit is above atmospheric, that is, during theentire inspiratory phase, check valve means between said reservoir andsaid downstream conduit preventing flow back from said reservoir to saiddownstream conduit, valve means sensitive to the pressure in saidreservoir for connecting said command signal conduit and said gas supplyconduit and for disconnecting them when the pressure in said reservoiris above a predetermined level, and bleed means actuated by the drop inpressure to atmospheric in said downstream conduit, for bleeding saidreservoir to atmospheric at a constant flow rate during said expiratoryphase.
 28. The ventilator of claim 15 wherein said ratio means comprisesfirst housing means divided into three chambers by first and seconddiaphragms, said first diaphragm being smaller in effective area thansaid second diaphragm, said first housing means having a first chamberbounded by said first diaphragm and having a first inlet connEcted tosaid gas supply conduit and a first outlet connected to said commandsignal conduit, a second chamber between said first and seconddiaphragms and connected to the atmosphere, a third chamber bounded bysaid second diaphragm and having a second inlet and a second outlet,first valve means connected to both said first and second diaphragms fornormally closing said first outlet, except when the pressure in saidthird chamber drops below a predetermined level, check valve meansconnected to said downstream conduit and connected through a restrictedorifice to said second inlet, to supply gas from said downstream conduitto said third chamber to gradually build up pressure therein during eachinspiratory phase, while preventing flow back from said third chamber tosaid downstream conduit, a pressure relief valve comprising secondhousing means divided by a third diaphragm into fourth and fifthchambers, said fourth chamber being connected to said downstream conduitand said fifth chamber having a third inlet connected to the secondoutlet and connected to atmosphere through an adjustable needle valve,the flow rate of which determines a limiting time ratio between theexpiratory phase and the inspiratory phase, third valve means connectedto said third diaphragm for opening and closing said third inlet, andspring means urging said third valve means away from closing said thirdinlet, said third inlet being held closed by the pressure in saiddownstream conduit until said pressure drops to atmospheric at the endof said inspiratory phase, said third inlet being open during theexpiratory phase.
 29. A ventilator for pressure-controlled operationwith an inspiratory phase and an expiratory phase, including incombination: a gas supply conduit for supplying a breathable gas underpressure, a downstream conduit, a command signal conduit, an airwayconduit suitable for connection to a patient, main valve means connectedto said command signal conduit for connecting said gas supply conduit tosaid downstream conduit during each said inspiratory phase when thepressure in said command signal conduit reaches a first predeterminedpressure level and for closing off said downstream conduit from said gassupply conduit during each said expiratory phase when the pressure insaid command signal conduit drops below a second, lower pressure level,sensitivity control means connected to said airway conduit forconnecting said gas supply conduit to said command signal conduit andthereby to raise the pressure in said command signal conduit to saidfirst predetermined pressure level when the pressure in said airwayconduit drops due to the commencement by a patient of an inspiratoryphase, to a third predetermined pressure level, and to close off saidcommand signal conduit from said gas supply conduit when the pressure insaid airway conduit rises above said third predetermined pressure level,means, actuated by the pressure in said airway conduit rising to afourth predetermined pressure level, for bleeding said command signalconduit to atmosphere, as upon commencement of said expiratory phase,means connected to said command signal conduit for bleeding saiddownstream conduit to atmosphere when said command signal conduitpressure drops below said second predetermined pressure level as at thebeginning of said expiratory phase, and flow control means connectingsaid downstream conduit to said airway conduit according to apredetermined flow pattern, with a peak flow rate at the commencement ofeach said inspiratory phase and a flow rate gradually diminishing to alower terminal flow rate according to said pattern.
 30. The ventilatorof claim 29 having means for varying said predetermined flow pattern bychanging the peak flow rate without changing the terminal rate.
 31. Theventilator of claim 29 wherein said flow control means comprises: firstflow means for providing a minimum constant flow from said downsTreamconduit to said airway conduit, second flow means for providing anadjustable initial peak flow from said downstream conduit to said airwayconduit, and means responsive to the pressure in said airway conduit forcontinually reducing the flow through said second flow means from saidpeak flow as the pressure in said airway conduit increases.
 32. Theventilator of claim 31 wherein said first flow means includes means forvarying the minimum constant flow.
 33. The ventilator of claim 29wherein said flow control means comprises: a housing divided by adiaphragm and a partition into first, second, and third chambers, saidfirst chamber being open to the atmosphere and bounded by saiddiaphragm, said second chamber being between said diaphragm and saidpartition and having an inlet connected to said downstream conduitthrough an adjustable needle valve to deliver said minimal terminalflow, and an outlet connected to said airway conduit, said third chamberhaving an inlet connected directly to said downstream conduit, saidpartition having an opening therethrough connecting said second andthird chambers, valve means for opening and closing said opening andconnected to and controlled by said diaphragm, spring means in saidhousing for exerting pressure on said diaphragm, and compression meansconnected to said spring means for compressing said spring means forvarying its pressure on said diaphragm, the pressure in said airwayconduit and in said second chamber acting on said diaphragm and tendingto close said valve means.
 34. A ventilator for providing breathing gasto a patient during an inspiratory phase and letting him exhale duringan expiratory phase, including in combination: a gas supply conduit forsupplying a breathable gas under pressure, a downstream conduit, acommand signal conduit, an airway conduit suitable for connection to apatient, means connecting said downstream conduit to said airwayconduit, main valve means connected to said command signal conduit forconnecting said gas supply conduit to said downstream conduit duringeach said inspiratory phase when the pressure in said command signalconduit rises above a first predetermined pressure level, and forclosing off said downstream conduit from said gas supply conduit duringeach said expiratory phase when the pressure in said command signalconduit drops below a second, lower, predetermined pressure level,phase-actuation means connected to said command signal conduit forterminating each said inspiratory phase and commencing a said expiratoryphase, by bleeding said command signal conduit to atmosphere, meansconnected to said command signal conduit for bleeding said downstreamconduit to atmosphere when said command signal conduit pressure dropsbelow said second predetermined pressure level at the commencement ofsaid expiratory phase, ratio means connected to said command signalconduit, said downstream conduit and said gas supply conduit for endingthe expiratory phase and initiating a new inspiratory phase byincreasing the pressure in said command signal conduit above said firstpredetermined pressure level by supplying gas from said gas supplyconduit to said command signal conduit, after a lapse of time followingthe commencement of said expiratory phase, said ratio means having meansfor sensing the duration of each inspiratory phase and for establishinga maximum duration of the succeeding expiratory phase as a time ratio ofthe inspiratory phase to the next succeeding expiratory phase, pneumatictiming means connected to said gas supply conduit, and sigh meansconnected to said phase actuation means and actuated by said pneumatictiming means at intervals longer than the inspiratory-expiratory cycleof the ventilator as controlled without said pneumatic timing means bysaid phase actuation means and said ratio means, for causing a longerinspiratory phase than usual and a greater volume than usual.
 35. Theventilator of claim 34 wherein said pneumatic timing means comprises aneedle valve connected to said gas supply conduit, a pressure-actuatedvalve downstream of said needle valve and having a fixed-capacitychamber wherein the pressure builds up from atmospheric to the pressurefor actuating said pressure-actuated valve, and means for bleeding saidchamber to atmosphere after actuation of said pressure actuated valve.36. The ventilator of claim 34 wherein said phase-actuation means isconnected to said airway conduit and is actuated by the pressure in saidairway conduit reaching a third predetermined pressure level and meansactuated by said pneumatic timing means for raising said thirdpredetermined pressure level to a fourth higher predetermined pressurelevel for a single inspiratory phase.
 37. The ventilator of claim 34wherein the means for connecting said downstream conduit to said airwayconduit comprises means for determining the volume of gas to pass fromsaid downstream conduit into said airway conduit during each inspiratoryphase, means for determining the time over which said volume is to bedelivered, and means for actuating said phase-actuation means at theconclusion of that said time, and means actuated by said pneumatictiming means for continuing to supply said gas to said airway conduitfrom said downstream conduit for an additional time, thereby increasingthe volume of a single inspiratory phase by a predetermined percent. 38.The ventilator of claim 34 wherein the means for connecting saiddownstream conduit to said airway conduit comprises means fordetermining the volume of gas to pass from said downstream conduit intosaid airway conduit during each inspiratory phase, means for determiningthe time over which said volume is to be delivered, and means foractuating said phase-actuation means at the conclusion of that saidtime, and means actuated by said pneumatic timing means for increasingthe volume of a single inspiratory phase by a predetermined andadjustable percent of the volume set by said means for determining thevolume.
 39. The ventilator of claim 34 wherein the means for connectingsaid downstream conduit to said airway conduit comprises means fordetermining the volume of gas to pass from said downstream conduit intosaid airway conduit during each inspiratory phase, means for determiningthe time over which said volume is to be delivered, and means foractuating said phase-actuation means at the conclusion of that saidtime, and wherein said pneumatic timing means generates a trigger signalwhen the sigh-frequency time is reached and said ventilator is in a saidexpiratory phase, means actuated by said trigger signal for resettingthe sigh frequency timer to zero, time lengthening means actuated bysaid trigger signal for lengthening the time set by said means fordetermining the time so that the connection between said downstreamconduit and said airway conduit is maintained during the additionaltime, for maintaining the trigger signal as the ventilator changes fromits expiratory phase to its inspiratory phase, means for returning saidtrigger signal to a zero value as the ventilator changes from that saidinspiratory phase to its next expiratory phase, means actuated when saidtrigger signal returns to zero for starting the sigh frequency timer ona new cycle and closing off said time lengthening means from said meansdetermining the time.
 40. The ventilator of claim 34 wherein said sighmeans includes: sigh volume control means for determining the additionalvolume delivered during said longer inspiratory phase, a main controlvalve connected to said pneumatic timing means and initiated thereby,and connected to said gas supply conduit and delivering a limited supplyof gas directly therefrom when initiated, a communication control valveactuated when said main control valve delivers said gas from said gassupply conduit upon said initiation, said communication control valvebeing connected to phase-actuation means and acting when actuated todelay the termination of the next said inspiratory phase, and resetvalve means connected to said main control valve and to saidcommunication control valve for resetting them upon completion of saidnext inspiratory phase to the position and pressure they had prior tosaid initiation, and connected to said pneumatic timing means forinitiating a new timing interval thereby upon completion of said nextinspiratory phase.
 41. The ventilator of claim 40 wherein said maincontrol valve is connected to said downstream conduit and is biasedthereby against initiation so long as the pressure in said downstreamconduit is above atmospheric, thereby preventing the master controlvalve from being initiated during an inspiratory phase.
 42. A ventilatorfor pressure-controlled operation with an inspiratory phase and anexpiratory phase, including in combination: a gas supply conduit forsupplying a breathable gas under pressure, a downstream conduit, acommand signal conduit, an airway conduit suitable for connection to apatient, means connecting said downstream conduit to said airwayconduit, main valve means connected to said command signal conduit forconnecting said gas supply conduit to said downstream conduit duringeach said inspiratory phase when the pressure in said command signalconduit rises above a first predetermined pressure level and for closingoff said downstream conduit from said gas supply conduit during eachsaid expiratory phase when the pressure in said command signal conduitdrops below a second, lower predetermined pressure level, sensitivitycontrol means connected to said airway conduit for connecting said gassupply conduit to said command signal conduit and thereby to raise thepressure therein above said first predetermined pressure level when thepressure in said airway conduit drops below a third predeterminedpressure level due to the commencement by a patient of an inspiratoryphase, and to close off said command signal conduit from said gas supplyconduit when the pressure in said airway conduit rises above said thirdpredetermined pressure level, means for bleeding said command signalconduit to atmosphere actuated by the pressure in said airway conduitreaching a fourth predetermined pressure level, as upon commencement ofan expiratory phase, means connected to said command signal conduit forbleeding said downstream conduit to atmosphere when said command signalconduit pressure drops below said second predetermined pressure level,as at the beginning of said expiratory phase, ratio means connected tosaid command signal conduit, said downstream conduit and said gas supplyconduit for ending said expiratory phase and initiating a newinspiratory phase by increasing the pressure in said command signalconduit above said first predetermined pressure level by supplying gasfrom said gas supply conduit to said command signal conduit, if thepatient fails to initiate a new inspiratory phase for himself, after atime lapse following the commencement of a said expiratory phase, saidratio means having means for sensing the duration of each inspiratoryphase and for establishing automatically a maximum duration of thesucceeding expiratory phase as a time ratio of the inspiratory phase tothe next succeeding expiratory phase, pneumatic timing means connectedto said gas supply conduit, and sigh means connected to said means forbleeding said command signal conduit and actuated by said pneumatictiming means at intervals longer than the inspiratory-expiratory cycleof the ventilator as controlled without said pneumatic timing means bysaid phase actuation means and said ratio means, for raising theactuating pressure level of said means for bleeding said command signalconduit above said fourtH predetermined pressure level, to a higherfifth pressure level.
 43. The ventilator of claim 42 wherein saidpneumatic timing means comprises a needle valve connected to said gassupply conduit, a pressure-actuated main sigh control valve downstreamof said needle valve and having a fixed-capacity chamber wherein thepressure builds up from atmospheric to the pressure for actuating saidmain sigh control valve, and means for bleeding said chamber toatmosphere after actuation of said main sigh control valve.
 44. Theventilator of claim 43 wherein said sigh means comprises a communicationcontrol valve connected to said main sigh control valve and actuatedthereby when downstream pressure therefrom is above atmospheric forconnecting said airway conduit to said means for bleeding said commandsignal conduit to supply the pressure to raise said pressure from saidfourth level to said fifth level, and means, actuated by said means forbleeding said downstream conduit, for de-actuating said communicationcontrol valve, disconnecting it from said airway conduit, and forbleeding to atmospheric the connection therefrom to said means forbleeding said command signal conduit.
 45. The ventilator of claim 43wherein said main sigh control valve is connected to and biased by saiddownstream conduit to prevent its actuation when said downstream conduitis above atmospheric pressure.